Today's Top Science Headline: "The Microbial Eve" --Paleo-Biologists Track Our Origins Back to Single-Celled Organisms
We now know that all extant living creatures derive from a single common ancestor, called LUCA, the Last Universal Common Ancestor. It's hard to think of a more unifying view of life. All living creatures are linked to a single-celled creature, the root to the complex-branching tree of life. If we could play the movie of life backwards, we would find this little fellow at the starting point, the sole actor in what would become a very dramatic story, lasting some 4 billion years.
There were, very possibly, other life forms before LUCA, reports NPR. We don't know exactly who LUCA was, or when it thrived. But paleo-biologists — scientists that investigate creatures that lived a long time ago — have succeeded brilliantly in mapping life's evolution from bottom-up in extraordinary detail, especially considering the difficulties in finding fossil evidence of creatures living billions of years ago.
Instead of looking for bones or imprints in rocks, to find LUCA they look at DNA. They are able to trace LUCA to a simple prokaryotic creature (a single-celled bacterium with unprotected genetic material) that lived some three billion years ago. It must have been a very tough organism, able to survive in very extreme environments.
Evolutionary biologist William Martin, from Heinrich Heine University in Düsseldorf, Germany, tried to track down LUCA in the genes of bacteria and archaea. This is not an easy task, as organisms often swap genes, making it hard to know what came from a very ancient lineage and what was picked up more recently.
The tree of life is pretty complicated. However, if you look at the picture, you will learn two important things: first, that humans and other animals are the absolute minority, a twig at the bottom right as part of the eukaryotes, organisms with cells that have DNA as genetic material protected by a membrane. (Eukaryotes include animals, planets, fungi, and protozoans.) Second, that the vast majority of living creatures are bacteria.
Next to the eukaryotes you will find the archaea, also single-celled organisms that are able to survive in extreme environments, such as near hot underwater thermal vents or oxygen-free wetlands. All evidence indicates that LUCA was a primitive form of archaea.
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